A major goal of our laboratory is to try to understand the roles amines and peptides serve in neuronal function. Towards that goal, over the last 15 years, we have developed a model system that involves two amines, octopamine and serotonin, and several peptides, proctolin, TNRNFLRFamide and peptide G1 (a peptide that specifically turns of cGMP metabolism in lobsters), whose functions we have been studying at multiple levels of organization in the lobster nervous system. This application focusses on specific subsets of octopamine- and serotonin-containing neurons found in the lobster ventral nerve cord (CNS), explores their physiological properties, and examines their possible roles in aggressive behavior. One great virtue of invertebrate model systems is that detailed analyses can be performed of the biochemical and physiological properties and functional roles of single identified neurons. We take advantage of that virtue with the present application, which asks the following specific questions. (1) How are a specific subset of serotonin-containing neurons concerned with postural regulation activated, and what factors regulate their firing rate? (2) Can we identify the specific subset of octopamine-containing neurons concerned with postural regulation? (3) How are these neurons activated and what factors influence their firing rate? (4) How do octopamine- containing neurons interact with serotonin-containing neurons? (5) Does interference with amine neuron function influence the aggressive status or position in a hierarchy of behaving lobsters? (6) Are the properties of amine neurons changes or is there any alteration in amine levels in lobsters as a result of behavioral interactions, like the establishment of a hierarchy? (7) Do amine levels change in individual neurons during a molt cycle or with growth and development of animals? Understanding amine-neuron function in the CNS remains a challenging and important area of investigation. We know that drugs that interfere with amine actions or metabolism can have profound effects on human behavior (Eg. cocaine, LSD, amphetamines), and in some cases we know or strongly suspect that abnormal amine-neuron function is the cause of a major neurological disorder (Eg. the loss of dopamine neurons and Parkinson's disease, excess dopamine and schizophrenia, norepinephrine and serotonin levels and major depressive illness, serotonin levels and sleep disorders). Our studies focus on the possible role of amine neurons in aggressive behavior in lobsters. As such they offer a potential biological model which may be of some use in understanding the complex social issue of violent behavior.